The present invention relates to medical devices, in particular bone and dental implants.
Medical devices which are implanted in a patient's body, e.g., orthopedic and dental implants, are typically coated to improve their biocompatibility and to promote fixation of the implant to the bone. In recent years, such devices have been commercially coated with hydroxyapatite. These coatings provide a surface suitable for the ingrowth of bone tissue, resulting in more secure fixation of the implant to the existing bone.
Hydroxyapatite coatings are commercially applied by thermal plasma spraying. Plasma sprayed coatings are generally thick, e.g., about 50 to 70 microns, porous, and only moderately well adhered to the implant. These coatings tend to enhance the quality of the bone-implant interface. However, the sprayed coatings may lack mechanical strength, resistance to dissolution, and may be difficult to apply to irregular surfaces, as spraying is generally a line-of-sight process.
Ion beam sputtering has been proposed as a method of coating medical implants with hydroxyapatite, e.g., as described in U.S. Pat. Nos. 4,944,754 and 4,908,754. However, ion beam sputtering does not allow the chemical composition and physical properties of the coating to be readily controlled.